Decrease In Maximum Temperature Research Articles

Thermal Runaway Characteristics of Ni-Rich Lithium-Ion Batteries Employing Triphenyl Phosphate-Based Electrolytes

Abstract Enhancing the safety performance of high-energy-density lithium-ion batteries is crucial for their widespread adoption. Herein, a cost-effective and highly efficient electrolyte additive, triphenyl phosphate (TPP), demonstrates flame-retardant properties by scavenging hydrogen radicals in the flame, thereby inhibiting chain reactions and flame propagation to enhance the safety performance of graphite/LiNi0.8Co0.1Mn0.1O2 (Gr/NCM811) pouch cells. The results reveal that the capacity retention of cells without flame retardants, and those with the addition of 1 wt%, 3 wt%, 5 wt%, and 10 wt% TPP is 96.4%, 92.1%, 84.15%, 40.8%, and 12.4% (at 1/2C 300 cycles), respectively. Furthermore, compared to cells without flame retardants, the highest temperature during thermal runaway (TR) decreases by 8.3%, 26.9%, 35.1%, and 38.8% with the addition of 1 wt%, 3 wt%, 5 wt%, and 10 wt% TPP, respectively. Through comprehensive analysis of the impact of flame-retardant additives on battery electrochemical performance and safety, it is determined that the optimal addition amount is 3 wt%. At this level, there are no significant flames during battery abuse, the triggering temperature for TR increases by 26.6 ℃, and the maximum temperature decreases by 157 ℃. Moreover, even after 300 cycles at 1/2C, a capacity of 814.5 mAh is retained, with a capacity retention rate of 84.1%. This study provides valuable insights into mitigating TR in high-energy-density power batteries.

Numerical assessment of hydrothermal and entropy generation characteristics of graphene quantum dots nanofluid in a microchannel heat sink incorporating secondary channels and ribs

Efficient heat dissipation from electronic chips is essential for enhancing their performance and longevity. Significant progress has been achieved through the introduction of nanofluids and microchannel heat sinks. However, there is still a need for nanofluids that demonstrate exceptional thermal properties and stability. Graphene quantum dots nanofluid, an innovative carbon-based coolant with zero-dimensional nanostructures, presents promising features such as excellent chemical stability, surfactant-free preparation, superior thermal properties, and minimal impact on rheological characteristics. This study explores, for the first time, the hydrothermal behavior and entropy generation of graphene quantum dots nanofluid in a microchannel heat sink comprising secondary flow channels and ribs. To this end, a three-dimensional conjugate heat transfer model is built using ANSYS Fluent software, and the governing equations are solved using the finite volume method. The simulations are carried out considering temperature-dependent thermophysical properties under different concentrations ranging from 0 to 0.5 % and Reynolds numbers ranging from 100 to 500. The results reveal that the maximum bottom wall surface temperature decreases by 5.88 K, while the heat transfer coefficient improves by 24.9 % compared to the base fluid. Moreover, the total entropy generation reduces by 14.7 %. On the other hand, the pressure drop increases by 43 %. Overall, the highest increment in Performance Evaluation Criteria is 10.8 % at a Reynolds number of 100 and a concentration of 0.5 %, making this particular condition suitable for practical applications.

Experimental study on a dual synthetic jets liquid cooling device

To address the growing heat dissipation requirements of high heat flux electronic devices, this work presents experimental research on a dual synthetic jets (DSJ) liquid cooling device. The effects of different heat flux, channel inlet flow rates, driving frequencies, and other parameters on the device ability have been explored. The experimental results indicate that the wall temperature increases by increasing the heat flux. Raising the channel inlet flow rate will reduce wall temperature. When DSJ is off, increasing the inlet flow rate from 0.16 L/min to 0.40 L/min results in a maximum temperature decrease of 6.30 °C and a pressure drop increase of 2.20 kPa. There is essentially no change in the pressure drop when DSJ is operating. When the inlet flow rate is 0.16 L/min, the maximum wall temperature at DSJ on is reduced by 6.83 °C compared with DSJ off. The convective heat transfer coefficient was raised by 40.55%. The vibrating diaphragm exhibits better low-frequency characteristics when working underwater. The convective heat transfer coefficient increases by 36.46% when the driving frequency is 20 Hz. Increasing the driving voltage, the device cooling performance increased. By increasing the driving voltage to 240 V, the wall temperature decreased by 6.30 °C, a decrease of 13.82%, and the convective heat transfer coefficient raised by 28.51%. The device overall performance increased by a maximum of 39.55% after DSJ on compared with DSJ off.

Optimization of the PVT performance with various orientations of jets and MFFNN-RSA prediction model for smart buildings

The combined thermal and photovoltaic technology in PV/T systems is considered as a greatly promising technology for smart buildings. Thus, investigations for enhancing the PV/T performance are still proceeding. This research presents an investigation for novel configurations of cooling jets for the PVT system. The linear and circular distribution for the inlet jets considering regular and irregular positioning for all the jets as new cooling configurations are implemented. Moreover, the proposed geometrical configurations are optemized regarding the performance to identify the most suitable configuration that achieves the optimum efficiency and temperature. Furthermore, a novel hybrid ANN model is presented for predicting the performance of the PVT systems. This model combines the multi-feedforward neural network (MFFNN) with an optimization technique called reptile search algorithm (RSA). The proposed model can process the studied parameters to predict the PVT performance parameters (top surface temperature, temperature un-uniformity, outlet temperature, and efficiencies). The proposed MFFNN-RSA model minimized the mean square error to less than 0.4857×10-3. The maximum temperature decrease achieved by the presented configuration reached 60.62K compared to the uncooled case, while the minimum temperature un-uniformity reached 1K and 6K for 400 and 1000 W/m2, respectively. The increase of the ambient temperature found to decrease the temperature un-uniformity in all the cases. The irregular jet with the linear distribution was found to achieve the optimum performance of the overall, thermal, and electrical efficiencies of 63.5%, 49.6%, and 14.25%, respectively. Furthermore, the electricity production cost was reduced by 11.6%, and the yearly CO2 emissions were reduced by 215.3 kg/m2 compared to the normal PV system. The proposed irregular-line distribution of the jets is found to be the best configuration regarding the temperature of the PV model and the overall efficiency considering the pumping losses.

Effect of oxy-fuel combustion with different O2/CO2 fractions on the pulverized coal combustion mechanism and heat transfer characteristics in rotary kilns: A numerical simulation study

Oxy-fuel combustion combined with carbon capture and storage is the most effective and direct technology to achieve carbon neutrality in cement industry. In this work, numerical simulation was employed to investigate the effects of air combustion and oxy-fuel combustion with different O2/CO2 fractions on the airflow field, temperature field, pulverized coal combustion mechanism, heat transfer characteristics and NOx distribution in rotary kiln. The results show that the airflow field under different conditions has no significant change. When transitioning from the air condition to the oxy-fuel condition, the ignition point of pulverized coal extends backward by approximately 0.2 m. The maximum temperature decreases from 2306 K to 2052 K, and the temperature becomes more uniform. As the oxygen concentration in the primary air increases, both the maximum and average temperatures gradually rise, and the flame length shortens from 25.4 m to 24.16 m. In the rotary kiln, the locations of char oxidation and gasification reactions differ, but these reaction locations remain consistent under different conditions. Under oxy-fuel conditions, the oxidation rate and oxidation proportion of char decrease, while the gasification rate and gasification proportion of char increase, resulting in a shortening of the burnout distance of coal from 34.5 m to 31.3 m. With increasing oxygen concentration in the primary air, the rates of char oxidation and gasification gradually rise, further shortening the burnout distance. The decrease in temperature at the front end of the rotary kiln under oxy-fuel conditions reduces the total heat transfer in the burning zone by 15 %. When the oxygen content of the primary air is 70 %, it ensures stable calcination of clinker. Additionally, under oxy-fuel conditions, the NOx generation is significantly reduced. With the increase of oxygen concentration in the primary air, the NOx concentration at the outlet decreases slightly from 451 ppm to 406 ppm, due to the increase in kiln temperature that favors the reduction of fuel NOx.

Examining the role of biophysical feedbacks on simulated temperature extremes during the Tinderbox Drought and Black Summer bushfires in southeast Australia

The Tinderbox Drought (2017–2019) was one of the most severe droughts recorded in Australia. The extreme summer air temperatures (>40 °C) combined with drought, contributed to the unprecedented Black Summer bushfires in 2019–20 over southeast Australia. Whilst the temperature extremes were largely driven by synoptic processes, it is important to understand to what extent interactions between land and atmosphere played a role. In this study, we use the WRF-LIS-CABLE land-atmosphere coupled model to examine the impacts of changes in leaf area index (LAI) and albedo by contrasting simulations with climatological and time-varying LAI and albedo. We analyse the impact of these biophysical feedbacks on temperature extremes and fire risk during the Tinderbox Drought and the Black Summer bushfires. Remote-sensing data showed a decrease in LAI (0.1–4.0 m2 m−2) over the three years of the drought along the southeast coast of Australia relative to the long-term climatology, while albedo increased inland (0.02–0.14). These changes in LAI and albedo were accompanied by an overall decrease in daily maximum temperature (Tmax) in the vast majority of interior regions (by ∼0.5 °C) and, in the 2019–20 summer, by a clear increase in Tmax in the coastal regions of up to ∼1 °C. Increased albedo explained most of the decreases in Tmax inland, whereas increases in Tmax along the coasts were mostly associated with LAI declines. The magnitude of the impact of biophysical changes on temperature demonstrates the potential impact that would be missed in simulations that assumed fixed vegetation properties. Finally, we only found a small impact from LAI and albedo changes on the fire risk (as measured by the fuel moisture index) preceding the Black Summer bushfires, suggesting these biophysical feedbacks did not significantly modulate fire risk. Our results have implications for coupled simulations relying on climatological LAI and albedo, including operation weather and seasonal climate predictions.

Time Series Analysis: Associations Between Temperature and Primary Care Utilization in Philadelphia, Pennsylvania

IntroductionEarth's temperature has risen by an average of 0.11°Fahrenheit per decade since 1850 and experts predict continued global warming. Studies have shown that exposure to extreme temperatures is associated with adverse health outcomes. Missed primary care visits can lead to incomplete preventive health screenings and unmanaged chronic diseases. This study examines the associations between extreme temperature conditions and primary care utilization among adult Philadelphians. Methods1,048,575 appointments from 91,580 patients age ≥ 18 years enrolled in the study at thirteen university-based outpatient clinics in Philadelphia from January 1, 2009, to December 31, 2019. Statistical analysis was performed from June to December 2023. Data on attended and missed appointments was linked with measures of daily maximum temperature and precipitation, stratified by warm and cold seasons. Sociodemographic variables and associations with chronic disease status were explored. ResultsRates of missed appointments increased by 0.72% for every 1°F decrease in daily maximum temperatures below 39°F and increased by 0.64% for every 1°F increase above 89°F. Individuals≥65 years and those with chronic conditions had stronger associations with an increased rate of missed appointments. ConclusionsTemperature extremes were associated with higher rates of missed primary care appointments. Individuals with chronic diseases were more likely to have missed appointments associated with extreme temperatures. The findings suggest the need for primary care physicians to explore different modes of care delivery to support vulnerable populations, such as making telemedicine during extreme weather events a viable and affordable option.

Numerical simulation, ANN training and predictive analysis of phase change material with 3D printing lattice structures

This study simulated and analysed the performance of phase change material with three lattice structures, i.e., simple cubic, body-centered cubic, and face-centered cubic, at various porosities and heat fluxes. Three parameters are analysed, including the maximum temperature of the heated wall, melting and solidifying times of PCM. The findings suggest that as the porosity rises, the maximum temperature decreases, while the increase in heat flux leads to a higher maximum temperature. Both the melting and solidifying times extend as porosity increases. An artificial neural network trained by the Levenberg-Marquardt algorithm is used to predict these three parameters. The lattice structure type, porosity, and heat flux are established as the input parameters for the network. The ANN predictions demonstrated outstanding performance in estimating these parameters with a minimum MSE of 0.00015 and a maximum R of 0.99899. The trained ANN is used to predict the crucial parameters of PCM with 82% SC, BCC, and FCC lattice structures. An excellent agreement is observed between the ANN predicted results and the simulation outcomes with a maximum relative error of 9.43%.

Computational investigation of the effect of geometry and fuel composition on the performance of a solid oxide fuel cell

The need to reduce the consumption of fossil fuels due to their negative impact on the quality of the air and on the greenhouse effect is causing major changes in the energy sector, with a progressively greater contribution of renewable energy sources to satisfy the global energy demand. Fuel cell technology is emerging as a key player in the energy transition since fuel cells convert directly chemical energy to electricity and heat without pollutant emissions. Among the different types available, solid oxide fuel cells (SOFC) can operate at high temperatures (up to 1000ºC), leading to high efficiency and stability. This work is concerned with the computational investigation of a planar solid oxide fuel cell. The governing conservation equations for mass, momentum, energy, species transport and electric charge are solved for a three-dimensional planar fuel cell. Different fuel and oxidizer compositions are considered and their influence on the performance of the fuel cell is investigated. The results show that when the hydrogen molar fraction in the fuel decreases, the maximum power and temperature decrease. The power, the efficiency and the maximum temperature are greater when the oxidizer is oxygen rather than air. The influence of the geometry of the air and fuel channels is also assessed, namely the dimensions of the channels and the effect of steps and obstacles in those channels.

The hypothermic effect of the antihypoxant 2-aminobenztiazole

BACKGROUND: One of the compounds studied at the Department of Pharmacology of the Kirov Military Medical Academy is a compound with a proven antihypoxic effect of 2-aminobenzothiazole (2-ABT). The mechanism of action of this substance is partially associated with the central action, and its protective effect may potentially be due to the general hypothermic effect.
 AIM: To determine the effect of 2-ABT on body temperature.
 MATERIALS AND METHODS: Experiments were carried out on 24 adult males of white outbred mice. 2-ABT was previously dissolved in 0.9% sodium chloride solution and administered intraperitoneally to mice at doses of 32.5 mg/kg (with proven antihypoxic effect), 21.7 mg/kg or 10.8 mg/kg. Rectal temperature was measured with an electronic thermometer DT-623 (China) before administration of the test substance, as well as 5, 30 and 60 minutes after the injection.RESULTS: Compound 2-ABT has a pronounced dose-dependent hypothermic effect. This effect is maximally expressed in a dose in which the compound has a proven antihypoxic property – 32.5 mg/kg. The hypothermic effect manifests itself within 5 minutes after administration, the maximum decrease in body temperature is observed after 30 minutes, while the effect persists for an hour.
 CONCLUSION: 2-ABT may be a promising compound for the creation of a drug for drug-induced (controlled) hypothermia.

A Stretchable Thermoelectric Device based on Direct Ink Writing of Liquid Metal and Multi‐Layer Lamination

AbstractWearable thermoelectric devices are widely used due to their ability to generate heat and cool rapidly without the need for bulky external equipment. Researchers have explored methods to enhance flexibility and stretchability by incorporating liquid metal as an electrode. However, the challenge lies in the low thermal conductivity of the polymer, which hampers heating and cooling performance. Traditional methods, like molding and spraying, increase the thickness of both liquid metal and polymer channels, but this added thickness does not significantly improve the device's stretchability.[1, 2] To overcome these issues, this paper proposes a stretchable thermoelectric device (STED), which offers improved heating and cooling capabilities, as well as enhanced stretchability. To enhance the thermal conductivity of the polymer, Ag powder with varying particle sizes is mixed with the material. Additionally, the liquid metal is deposited using the direct ink writing (DIW) method, reducing the whole thickness of STED. The air layer is created by printing molten isomalt, which is subsequently removed using water. The proposed STED exhibits high stretchability, reaching up to 150 %, enabling flexible twisting in various directions. The double‐layer structure resulted in a maximum temperature decrease of 14 °C at room temperature.

Estimation of heat flux entering the bone during the drilling process using the inverse heat transfer method

Drilling is one of the most important surgical steps and bone fracture repair. In this step, the temperature may exceed 47 °C and thermal necrosis may occur, which has irreversible consequences. Knowing the amount of heat transferred to the bone and its changes can be effective in recognizing this heat damage and minimizing it. In this research, it was tried to estimate the amount of heat flux entering the bone during the drilling process using the inverse heat transfer method. Drilling tests were performed on cow bone samples and the temperature changes at the hole location were measured using the inverse heat conduction transfer method. The amount of heat input was estimated. The K-type thermocouple is used to measure temperature. The diaphysis fragment of the cow's thigh (middle part), which has a length of about 90 mm and the thickness of the cortical bone in this range is about 8–10 mm, was used. Also, to ease the tests, the beginning and end parts of the fresh femur were cut with a saw. The results show that the maximum heat flux occurs earlier than the maximum temperature. It was observed that the maximum heat flux and the maximum temperature rise with the increase of the rotational speed and the diameter of the tool. As the feed speed rises, first the maximum temperature and maximum heat flux decrease and then increase. By tripling the feed speed, the maximum heat flux decreases by about 20%. The highest percentage rise in temperature and heat flux occurs with a rise in rotational speed, which is around 130–140%. After the rotational speed, increasing the drill diameter increases the temperature up to about 66.7%. The results can be used to prevent thermal necrosis because the maximum heat flux is visible before the occurrence of the maximum temperature.

Climate drives of growth, yield and microclimate variability in multistoried coconut plantation in Konkan region of Maharashtra, India

Long term experiments (2013-14 to 2018-19) were conducted in Regional Coconut Research Station, Bhatye, a representative location of major coconut growing region of Maharashtra (Konkan region) to study the impact of changing weather parameters on growth and yield of 32 years old coconut plants (dwarf x tall, i.e., COD x WCT). Regression based trend analysis of weather parameters was conducted to check the variability of weather parameters over experimentation years. There was a decrease in maximum temperature (r2=0.034) and increase in minimum temperature (r2=0.017) and rainfall (r2=0.393), indicating change in weather parameters. Correlation studies were carried out to understand the interaction between weather parameters and coconut growth and yield. Maximum temperature had a negative impact on growth (-0.02 and -0.58 for number of leaves and annual leaf production) but had a positive impact on yield (0.41, 0.64 and 0.63 for number of bunches, number of buttons and nut yield). Minimum temperature had significant negative effect on annual leaf production (-0.88) and had a positive effect on nut yield per plant (0.95). The effect of relative humidity (morning and evening) was non-significant. Rainfall had its influence on the crop by negatively affecting the number of bunches (-0.10) and nut yield per plant (-0.48), a positively affecting number of buttons (0.08). Further, microclimate in the plantation was compared to an open field, which indicated lower maximum and minimum temperature (-3.4 and -3.1 %) and higher morning and evening relative humidity (1.6 and 1.9 %) in the coconut plantation as compared to the open field.

Study of an Active Heat‐Dissipating Liquid Metal Wire with Electrical‐Material Cotransmission Characteristics and Its Applications

In the field of precision motors, there is a growing demand for higher power density, requiring wires to withstand elevated current density and resulting,in significant heating of the motor. This study investigates various properties of liquid metal conductors and evaluates their potential for enhancing the heat dissipation performance in a motor armature system. The results demonstrate that liquid metal conductors can be successfully applied to a motor armature system. Their characteristics, such as electrohydraulic coupling and decoupling, fulfill the requirements of fluid field circulation and unidirectional electrical conduction in the armature system. With a current density of 176.8 mA cm−2, the maximum temperature decreases from 35.2 to 30.9 °C, achieving a temperature reduction of 12%. This article details the specific methods for manufacturing motor armatures using liquid metal conductors, including the structures of different types of armature systems. Additionally, the article also presents a study on some performance aspects of this armature system, showing a decrease in the maximum temperature from 54.9 to 50.9 °C, corresponding to a 7.3% temperature reduction. Thus, a novel approach is provided to the thermal management system of motors, which can be further extended to the field of bioelectrodes in future research.

Thermomagnetic convection control strategies for electromagnetic devices immersed in a ferrofluid

This paper presents new control strategies for improving the thermomagnetic convection intensity in electromagnetic devices. The system consists of a winding prototype immersed in a ferrofluid solution based on magnetic nanoparticles. The whole system is exposed to an external magnetic field generated by an annular magnet placed against the tank. When possible, experimental results are compared with numerical ones obtained using the finite element method in a 2D-axisymmetric setting. The first control strategy consists of assessing the impact of Curie’s temperature on heat removal. Numerical calculations show that the maximum winding temperature decreases by 2.2°C with the use of magnetic nanoparticles with the lowest Curie temperature. Employing an auxiliary magnetic field may be another method for monitoring the thermomagnetic convection. The number of streamlines increases in the upper part of the tank due to the intensification of the magnetic force at the top of the winding. It is shown that magnetization, orientation, and location of the magnet play a crucial role in maximizing heat transfer inside the tank. The experiment shows a temperature decrease of 9 °C at the top of the winding if an external magnetic field is applied.

Effect of Surface Reaction on the Distribution Characteristics of Temperature and OH Radicals in Microchannel Combustion

Microchannel burners suffer from low combustion efficiency and poor stability in applications. In order to explore the effect of wall reaction on methane/air premixed combustion performances in the microchannel, the effects of wall activity, inlet velocity, pressure, and equivalence ratio on the temperature and radical distribution characteristics were studied by CFD computational simulations. It is found that as the reaction pressure increases, there are more free-radical collisions, causing the reaction temperature to rise. The OH radicals participate in the reaction at the active near wall so that the mass fraction of the OH radical on the active wall is lower than that on the inert wall. As the equivalence ratio increases from 0.6 to 1.2, the high-temperature regions increase but the maximum temperature decreases. The mass fraction of OH radical increases with the increase of the equivalence ratio, and the increase of OH radical near the inert wall is larger than that of the active wall. As the flow rate increases, the disturbance increases, and the combustion reaction becomes more intense, resulting in an increase in the temperature and the mass fraction of OH radicals. The mass fraction of H, O, OH, and CH3 radicals in the inert wall was slightly higher than that in the active wall, in which the peak mass fraction of CH3 radical appeared at the axial position closest to the entrance, while the other three radicals reached the peak at about the same axial position. This study provides a reference for combustion stability in microcombustors.

Essential role of liquid phase on melt-processed GdBCO single-grain superconductors

We systematically investigated the role of additional liquid source (LS) which creates a liquid-rich nucleation environment and influences the growth kinetic energy. It enables a significant decrease in maximum processing temperature (Tmax) even close to the peritectic decomposition temperature (Tp), hence optimizing the distribution and size of the Gd2BaCuO5 (Gd211) particles. By exploiting this combined LS and low Tmax (LS+LTmax) growth method, the performance of GdBa2Cu3O7-δ (GdBCO) single-grain superconductors has been greatly improved. Therefore, the maximum trapped magnetic fields reach 0.746 T and 1.140 T for the 18- and 25-mm-diameter samples at 77 K. Meanwhile, superior flux pinning performance has been observed at the growth section boundaries (GSBs) with a decreased density of Gd211 particles in the LS+LTmax samples. These results indicate that the LS+LTmax technology can fabricate high-performance single-grain superconductors with improved reliability which is considered important for engineering applications.

Improved cooling of photovoltaic panels by natural convection flow in a channel with adiabatic extensions.

In hot dry regions, photovoltaic modules are exposed to excessive temperatures, which leads to a drop in performance and the risk of overheating. The present numerical study aims to evaluate the natural air cooling of PV modules by an inclined chimney mounted at the back. The basic equations were solved using the finite volume method. The validity of the model is verified by comparison with the data available in the literature. Thermal and dynamic flow patterns are analyzed for a variety of parameters: Rayleigh numbers from 102 to 106, PV panel tilt angle from 15° to 90°, and channel aspect ratios from 1/20 to 1/5. A critical aspect ratio has been determined to minimize overheating of the PV module. According to the computational results, the tilt angle and modified Rayleigh number increase the mass flow rate and mean Nusselt number. The overheating zone with maximum temperatures is located in the upper part of the photovoltaic panel. The addition of an extension to both channel's inlet and outlet was found to improve the cooling of the photovoltaic panels; however, only the extensions downstream of the channel are truly effective. The critical lengths at which channel performance improves significantly were identified by examining the impact of longer extensions on channel performance. Increasing the extension length from 0 to 3H improves the mass flow rate by 65%, the average Nusselt number by 13.4%, and leads to an 11% decrease in maximum temperature when Ra* = 106. This cooling technique is particularly promising for hot dry regions where water is scarce.

Numerical study of a composite cooling method for hypersonic aircraft

Thermal protection is a crucial issue for a long-flying hypersonic aircraft. In this work, a composite cooling method is proposed and implemented on a hypersonic blunt cone. The composite cooling method combines impinging and convective cooling at the cone head with transpiration cooling employed downstream to produce an overall cooling effect of the cone. Using computational fluid dynamics, the influences of the cooling gas and different attack angles on the cooling effect are examined. The results indicate that the combined cooling method can effectively reduce the overall outer wall temperature of the cone. In particular, with the combined cooling method, an increase in mass flow rate of the cooling gas has been observed in numerical tests, which results in a decrease in the head temperature. The maximum temperature decrease can reach 77.0% on the wall when the mass flow rate of the cooling stream is 1.1 kg/m2 s. The cooling performance on the leeward side can be better than that on the windward side for a fixed cooling gas mass flow rate. This gap in cooling performance between the two sides can be further amplified by a larger attack angle. Quantitatively, when using the combined cooling method, the temperature difference between the windward and leeward sides increases from 106 to 270 K when the attack angle increases from 4° to 8°. The numerical results in this study could provide theoretical and statistical guidance for the design of novel active thermal protection methods for hypersonic aircraft.

Local cooling and drying induced by Himalayan glaciers under global warming

Understanding the response of Himalayan glaciers to global warming is vital because of their role as a water source for the Asian subcontinent. However, great uncertainties still exist on the climate drivers of past and present glacier changes across scales. Here, we analyse continuous hourly climate station data from a glacierized elevation (Pyramid station, Mount Everest) since 1994 together with other ground observations and climate reanalysis. We show that a decrease in maximum air temperature and precipitation occurred during the last three decades at Pyramid in response to global warming. Reanalysis data suggest a broader occurrence of this effect in the glacierized areas of the Himalaya. We hypothesize that the counterintuitive cooling is caused by enhanced sensible heat exchange and the associated increase in glacier katabatic wind, which draws cool air downward from higher elevations. The stronger katabatic winds have also lowered the elevation of local wind convergence, thereby diminishing precipitation in glacial areas and negatively affecting glacier mass balance. This local cooling may have partially preserved glaciers from melting and could help protect the periglacial environment.